Precipitation of pure metallic copper from copper-bearing solutions



Aug. 4, 1953 E. s. ROBERTS 2,647,825

f A PRECIPITATION OP PURE METALLIC COPPER FROM COPPER-BEARING SOLUTIONSFiled April 8, 1949 Pressca/e /D/Pobacr BY I A cu POM/0f?? n l y TTORNEYPatented Aug. 4, 1953 PRECIPITATION OF PURE METALLIC COP- PER FROMCOPPER-BEARING SOLUTIONS Edward S. Roberts, New York, N. Y., as signorto Chemical Construction Corporation, New York, N. Y., a corporation ofDelaware Application April 8, 1949, Serial No. 86,156

11 Claims.

This invention relates to a process for the precipitation of coppermetal powder of very high purity. More particularly, the invention isconcerned with an improved continuous process for the precipitation atelevated temperatures and pressures of copper metal powder from aqueoussolutions of copper salts.

The present invention constitutes a continuation-in-part of my copendingapplication with Samuel Strelzof and William H. Baxter, Serial No.661,502, led April 12, 1946, now abandoned, entitled Method for theProduction of Copper.

Many processes have been suggested by which copper metal may berecovered from copper ores, low-grade copper, or other copper sources,by chemical treatment. All of these proposals, in addition to mechanicalconcentration, involve at least two broad chemical unit processes. Inthe first, the object is to separate the valuable metals from wastematerials, by dissolving the former in an aqueous solution, and thenseparating that solution, by mechanical means, from the waste solids. Inthe present discussion, this unit process will be referred to as thedissolving or solution operation. In the second of these, the object isto extract the metal values from the solutions so produced and to obtainthese metals in commercially desirable form. In the present discussion,this unit operation will be referred to as the precipitation and/orreduction operation.

The copper solutions to be treated may be obtained industrially in anumber of different ways. They may constitute copper mine waters, heapleaching solutions and the like. They may arise from ammoniacal leachingof oxide or carbonate ores, native copper-bearing ores, or secondaryscrap materials. They may arise from acid leaching of oxide, carbonate,or sulfide copper ores, or other products containing available copper.

`In the process of the present invention, only the precipitatingoperations are specifically dealt with. Since the invention is notconcerned with how copper is placed in solution as copper salts, thedissolving procedure will be referred to, generically, as noted above,as solution voperations.

The present invention is not concerned with their eiiciency or lack ofit, since no matter how satisfactory such an operation may be, it is oflittle practical value if the copper content of the solution cannot beeiiiciently and economically recovered. Unfortunately, all thepreviously proposed precipitating operations have suffered from one ormore defects.

In'the present copper industry, only one method of extracting purecopper' metal from solutions v of its salts has been industriallydeveloped to any particular extent. This is the electrowinning of copperthrough the use of insoluble anodes. This method, however, can be usedonly in connection with large and permanent leaching installations. Evenwhen electrodeposition is used, the copper cathodes so obtained must befurther refined in fusion operations and cast into bars before it ismarketable.

This type of operation, however, has resulted in setting the puritystandard for commercial copper. Copper, to be industrially acceptable,must meet so-called electrolytic standards, i. e., the copper content,plus the minor silver content, must be at least 991.9% by weight.

Commercially, previously proposed methods of chemical precipitation havefailed in that they cannot produce precipitated copper of this requisitedegree of purity. It is, therefore, the principal object of the presentinvention to develop a precipitation procedure not subject to theseobjections. A process in accordance with the objects of the presentinvention should be capable not only of producing copper in therequisite grade but should, in addition, be capable of producing thecopper in efficient recovery.

Surprisingly, in view of the inefiectiveness of previously-knownproposals, these objects have been fully met in a straightforwardprecipitating process. Brieily, the process incorporates (l) reductionof copper ions in solution to the cuprous condition by saturating thesolution with carbon monoxide at low temperatures and low or atmosphericpressures in the presence of copper metal; (2) removal of suspendedmatter and dissolved impurities; and (3) treatment of the saturated,claried solution at increased temperature and pressure in the presenceof an atmosphere containing reducing gas. Care is taken to precipitateonly a part of the available copper. All unprecipitated copper isrecycled.

In the accompanying drawing, there is shown a flow sheet which, it isbelieved, Will assist in understanding the description of the process ofthe present invention. The iiow sheet sets forth diagrammatically theprincipal operations of the present invention.

It is an advantage of the precipitating procedure of the present processthat it is applicable to solutions of copper salts obtained by anydesired process. They may include any of the operations listed above.Such operations form no part of the present invention. Accordingly,dissolving the copper is indicated on the flow sheet broadly as SolutionOperations.

Feed to the solution operation is indicated as containing copper-bearingsolids. Usually it will consist of low-grade copper, which requiresfurther purincation; and/or an ore of copper-bearing minerals. Lin thelatter case, it is ordinarily uneccnomical to treat ore as mined.Usually it will be pre-concentrated, as by washing, notation, gravityseparation, or the like. These preconcentration operations alsoconstitute known arts and form no part of the present invention.

Although, as noted above, the particular nature of the solutionoperations forms no part of the present process, they have beenindicated on the now sheet. This is necessary because the processinvolves a certain amount of recirculation. The feed, whatever itsnature, is treated by some known method to produce a solution containingcopper ions.

In most such solution operations, only a part of the material beingtreated is soluble. There will be a residue which ordinarily is wastematerial,

or ganffue, so far the solution is concerned. This material may betreated in other processes, if so desired. However, so far as thepresent invention is concerned, they are simply removed from thecircuit. This may be done by ltration, settling, or any other desirableprocedure. Since its exact nature -forms no part of the presentinvention, this mechanical separation of the solution from extraneouswaste material is considered to be part of the procedure designated onthe flow sheet as Solution Operations.

Claried solution so obtained is given the first actual treatment of thepresent invention. This is a reduction of copper to cuprous ions,carried out in some suitable tank or tanks with copper metal and carbonmonoxide. This treatment is highly important in the success of thepresent process. If it is omitted, production is unreliable both inquantity and quality. Without this treatment, results differ insuccessive runs, wherein conditions otherwise appear to be thesame. Useof this simple operation not only insures good but consistent results.

Most plants usually have available a source of low-grade copper metal.Preferably in comminuted form, it may be a recovery product, such ascement copper, or the like; or simply scrap from other operations. Itneed not be low-grade. Operation of the present process should not beconfused with earlier processes in which copper metal is dissolved and aportion thereof precipitated in higher purity. That operation can neverprecipitate as much copper as is dissolved. In the present process,copper metal is used as a reducing agent in treating dissolved copper.Eventually all dissolved copper is precipitated in high purity in thisinvention.

Clariiied solution is mixed with the metal and saturated. The treatingtemperature should be low, i. e., from room temperature to about 100 C.to insure the gas solubility. Crdinarily, liquor to be treated will beat a temperature below about 50,o C. Gas is ordinarily fed under justsufhcient pressure to meet fiow resistance. However, when anammonia-containing leach liquor is used, higher pressures, up to about100 pounds gauge, may be required to complete saturation.

Treatment is carried out in any suitable vessel or vessels. As shown,saturating is done in a separate vessel from the admixture with coppermetal. `Some time may elapse between the addition of the metal and ofthe gas. Thus, two tanks are shown to simplify the description andbecause their use may simplify operation in some cases, particularly ifsaturation is done under increased 4 pressure. However, both operationsmay be done successively or simultaneously in one vessel.

The resultant saturated slurry is now a composite mixture. It comprisesundissolved copper metal and the assorted iluids. Of the latter, thesolution of copper as cuprous ions is of primary importance. This slurryis then filtered, both the presscake and filtrate being subsequently andseparately treated.

Ordinarily, the presscake is directly returned to the SolutionOperations, to recycle its copper content. It may contain a considerablequantity of unused copper metal. If so, all or a part may be recycled tothe reduction operation. However, this is an optional procedure.Therefore, it is indicated by a dotted line on the flow sheet.

Continuing with the illustrative case, solution which is saturated withcarbon monoxide is then treated to precipitate a part or" its coppercontent. This is carried out in an autoclave, preferably of thecontinuous type, in which increased temperature and pressure is applied.Treatment conditions will vary somewhat, depending upon whether copperor copper-ammonium ions are present.

In either case, operable temperatures may be substantially the same.Generally, they should be above 100 C., and may range up to as high as275 C., or slightly above. However, for diierent solution operations,there are preferable temperature ranges. In the case of copper-ammoniumions, excessive temperature at low pressure favors precipitation ofcopper oxide and/or sulfide. With ammoniacal liquors a good practice isto utilize a temperature of from about llOl50 C. Somewhat highertemperatures are preferable in treating acid liquors. In this case, arange of from about 200300 C. appears to constitute the optimum.

In treatment of saturated solutions, the pressure chosen also is subjectto certain considerations. Pressures excessively above those necessaryat the operating temperature perform no useful function. Since theyrequire heavier apparatus, they should be avoided. In the case of acidleaching liquors, the utilisable pressure range is from about '75 to1000 pounds. For the preferred temperatures, however, this pressurerange will be from about 225-425 pounds. For ammoniacal leach liquors,however, or for solutions containing extraneous gases, pressures from300-700 pounds higher than those otherwise used may be found desirable.Because of' the variance in partial pressure of the ammonia, a goodaverage practice with ammoniacal liquors will generally lie between15S-'750 pounds.

Operation of the process of the present invention will be more fullyillustrated in conjunction with the following examples. The latter aregiven as illustrative only and not necessarily by way of limitation.Except as otherwise noted, all figures expressed in percent are byweight.

Example 1 To illustrate the treatment of copper solutions obtained byammoniacal leaching, the following experiment was performed. An impurecopper was leached with a liquor containing approximately 55.5 mols ofwater, 3.03 mols of CO2, 6.56 mols of ammonia and 1.21 mols of copper.Leaching was carried out until a gravity of about 1.22 was reached,corresponding to the addition to the liquor of about 0.48 mol of copperand 0.41 mol of oxygen. This solution was treated with copper metal andthe resultant slurry ltered. The

.filtrate was saturated with carbon monoxide at about C. and 35centimeters pressure and passed to an autoclave. In the latter, it'wastreated with carbon monoxide at about 100 pounds per square inchpressure, after which the temperature range was raised to 130 C. andheld for 2 hours, the pressure rising to a maximum of about 460 poundsper square inch. The treated product was cooled, pressure relieved andthe precipitated copper metal ltered out, surface treated by boiling insulfuric acid, dried, and analyzed.

About 28.4% of the copper entering the autoclave was precipitated aspowder, having an extraordinarily high purity of 99.99%. The remainingliquor was recirculated to the leaching operation.

' Example 2 The procedure of Example 1 was repeated, using precipitationtemperatures ranging from ll50 C. and pressures from 15G-750 pounds persquare inch. In each case, products were obtained which amounted to22-28% of the'copper content of the liquor after leaching. In each case,analysis of the product showed a copper content of 99.94 %-99.99

It should be noted that in the above treatments the product powder,after washing, was boiled Vwithsulfuric acid to prevent reoxidation.

Example 3 As illustrative of the application of the present invention tothe precipitation of copper from acid solutions, thefollowingexperiments were carried out. Y.

A notation concentrate containing oxidized copper minerals, copper suldeminerals and iron suliide minerals was subjected to oxidation at 225 C;and 600 'pounds per square inch in the presence of ferrie sulfate toobtain a solution of copper and Temperature and pressure weremaintainedfor i suiiicient time to precipitate about 60% of the available copper,the charge being then cooled and filtered, the ltered powder beingcollected, boiled with sulfuric acid, Washed and dried.

The rst portion so treated was found to yield about 62.2% of theavailable copper in a product analyzing 99.95% pure copper. Repeatingthe experiment on successive portions, at temperatures from 200-275 C.showed that temperatures above about 250 C. were not desirable and thatabove about 300 C. were impractical. In the temperature range from200-.250 C. and a total pressure of 300-700 pounds per square inch, ofwhich the partial pressure of the reducing gas is ordinarily about100-150 pounds per square inch, from 60-75% of the available copper wasprecipitated in grades analyzing 99.94 %-99.99% copper. The extent towhich precipitation is carried out is a critical limitation. It willdepend, however, to some extent, on the nature of the liquor beingtreated. This is shownin the above examples.

Using an ammoniacal leach in the solution operations, it is desirable toreturn thereto a considerable portion of the copper available forprecipitation in the autoclave. This is necessary to providecopper-ammonium complex in the leach liquor. Experience hasvshown thatprecipitation of about 20-'30% of the available copper entering theautoclave is good practice. Within this range in any one cycle, about95-105% of the copper taken up during leaching is precipitated in adegree of purity exceeding 99.94%, i. e., well above the minimum coppercontent required to meet electrolytic standards. The remainder isrecycled. For a series of cycles the total amount of precipitatedycopper will substantially balance the total amount dissolved duringleaching.

In precipitating from solutions obtained when the solution operationsinvolve acid leaching and/or acid-oxidation treatment or the like, thecirculating load of copper may be much less. There is no necessity forrecirculating any copper vions for the sake of the leaching operation.

However, experience has shown that for this type of operation, a goodpractice is to precipitate only -70% of the copper entering theautoclave. While it is obviously impossible to go much below 60%, it isnot economical to do so. In many cases, particularly in batchoperations, it is possible to exceed the '70 limitation for certainconditions. However, the solution to be treated will seldom have asolute content of only pure copper salts. Thereforey exceeding the '70%limit increases the likelihood of precipitating extraneous materialswith the copper; and therefore, adversely kaffecting the quality of theproduct. Actually, there is no loss, since all unprecipitated copperVmay be recirculated. Itz is, therefore, preferable that precipitationbe not carried above about the '70% limitation.

I claim:

1. In the process of recovering copper in high purity from solidcopper-bearing material wherein said material is treated by solutionoperations to obtain a solution containing cupric and cuprous `ions andcopper metal is chemically precipitated from resultant solution, theimprovement which comprises: contacting additional copper metal lwithsaid solution and at below 100 C., substantially saturating the liquidwith carbonv monoxide, whereby additional copper is introduced intosolution Vwith 'a concurrent equivalent reduction of cupricv tocuprousions; subjecting so-treated liquor, at a pressure of from about75 to about 1000 pounds per square inch and at least suicient to preventboiling of the solution and under an atmosphere comprising carbonmonoxide to a temperature above 100 C., but not more than 150 C. forammoniacal liquors and 300 C. for acid liquors, for suiiicient time toprecipitate at least an amount of copper metal powder greater than thatdissolved in reducing cupric to cuprous ions,

but not more than so much as is at least 99.9% copper; collectingprecipitated copper and recirculating residual copper to the solutionoperations.

2. In the process of recovering copper in high purity from solidcopper-bearing material wherein said material is treated by solutionoperations to obtain a solution containing cupric and cuprous ions andcopper metal is chemically precipitated from resultant solution, theimprovement which comprises; contacting said solution with additionalcopper metal in amount at least stoichiometrically equivalent to a majorportion of the cupric ions in solution and at below about 100 C.,substantially saturating the liquor with carbon monoxide, wherebyadditional copper is introduced into4 solution with a concurrentequivalent reduction of cupric to cuprous ions; subjecting so-treatedliquor, at increased pressure at least sufficient to prevent boiling ofthe solution, and under an atmosphere comprising carbon monoxide, to atemperature above about 100 C., but not more than about 150 C. forammcniacal liquors and 300 C. ior acid liquors, for suilicient time toprecipitate more copper than dissolved in the cupric-cuprous reductionstep, but not more than is at least 99.9% pure copper; collectingprecipitated copper and recirculating residual copper to the solutionoperations.

3. A process according to claim 2 wherein the solution operationsinvolve producing copperammonium ions in amrnoniacal liquor, furthercharacterized in that the precipitation of copper metal powder iscarried out at from about 110 C. to about 150 C. for sufficient time toprecipitate only so much metal powder as is at least 99.9% pure copper.

4. A process according to claim 3 wherein the pressure during metalpowder precipitation is from about 150 to about 750 pounds per squareinch.-

5. A process according to claim 3 in which about 20-'3070 of theavailable copper is precipitated.

6.- A process according to claim 2 wherein the solution operationsproduce copper ions in an acid solution of copper sulfate, furthercharacterized in that the precipitation of copper metal powder iscarried out at a temperature o about 200 C. to about 300 C., forsufficient time to precipitate only so much metal powder as is at least99.9% pure copper.

7. A process according to claim 6 wherein the pressure during reductionis from about 225 to about 425 pounds per square inch.

8. A process according to claim 6, in which from about 60-75% of theavailable copper is precipitated.

9. In a process for the preparation of copper metal powder by treatmentwith carbon monoxide of a solution containing copper ions, theimprovement which consists in: treating the solution with copper metalsto substantially reduce any cupric content to cuprous and substantiallysaturating the liquor with carbon monoxide at a temperature below about100 C. and subjecting the so-treated liquor at a temperature from about110 C. to about 300 C. under increased pressure, in an atmospherecomprising CO', for such time as is suicient to precipitate more copperthan said treating copper, but only copper having a purity of at least99.9% and collecting precipitated copper.

10. In a process for the preparation of copper metal powder by treatmentwith carbon monoxide of a solution containing copper ions, theimprovement which consists in: subjecting a solution containing cupricand cuprous ions and substantially saturated with carbon monoxide totreatment with copper metal to substantially reduce the cupric contentto cuprous, and then to a temperature from about 110 C. to about 300 C.,and under superatmospheric pressure, for such time as is sufcient toprecipitate more copper metal than said treating copper, but only copperhaving a purity of at least 99.9%, and collecting precipitated copper.

11. In a process for the preparation of copper metalv powder bytreatment with carbon monoxide of a solution containing copper ions, theimprovement which consists in; subjecting said solution containingc'upric and cuprous ions after it is treated with copper metal tosubstantially reduce the cupric content to cuprous, and substantiallysaturated with carbon monoxide, to a temperature from about 110 C. toabout 300 C, and under pressure of from about to about 1000 pounds persquare inch, for such time as is sufficient to precipitate more copperthan said treating copper, but only copper having a purity of at least99.9%, and collecting precipitated copper.

EDWARD S. ROBERTS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 924,076 Jumau June 8, 1909 1,686,391 Muller et al Oct. 2, 19281,763,781 I-Ieath et al June 17, 1930 2,008,373 Tobelmann July 16, 19352,227,783 Klurnpp Jan. 7, 1941 2,290,313 C'aron July 2l, 1942 FOREIGNPATENTS Yl\umber Country Date 24,163 Great Britain of 1911 OTHERREFERENCES A Comprehensive rIreatise on Inorganic and TheoreticalChemistry, vol. 3, pages 158 and 232, edited by Mellor, published in1923 by Longmans, Green and Co., London, England.

1. IN PROCESS OF RECOVERING COPPER IN HIGH PURITY FROM SOLIDCOPPER-BEARING MATERIAL WHEREIN SAID MATERIAL IS TREATED BY "SOLUTIONOPERATIONS" TO OBTAIN A SOLUTION CONTAINING CUPRIC AND CUPROUS IONS ANDCOPPER METAL IS CHEMICALLY PRECIPITATED FROM RESULTANT SOLUTION, THEIMPROVEMENT WHICH COMPRISES: CONTACTING ADDITIONAL COPPER METAL WITHSAID SOLUTION AND AT BELOW 100* C., SUBSTANTIALLY SATURATING THE LIQUIDWITH CARBON MONOXIDE, WHEREBY ADDITIONAL COPPER IS INTRODUCED INTOSOLUTION WITH A CONCURRENT EQUIVALENT REDUCTION OF CUPRIC TO CUPROUSIONS; SUBJECTING SO-TREATED LIQUOR, AT A PRESSURE OF FROM ABOUT 75 TOABOUT 1000 POUNDS PER SQUARE INCH AND AT LEAST SUFFICIENT TO PREVENTBOILING OF THE SOLUTION AND UNDER AN ATMOSPHERE COMPRISING CARBONMONOXIDE TO A TEMPERATURE ABOVE 100* C., BUT NOT MORE THAN 150* C. FORAMMONIACAL LIQUORS AND 300*. FOR ACID LIQUORS, FOR SUFFICIENT TIME TOPRECIPITATE AT LEAST AN AMOUNT OF COPPER METAL POWDER GREATER THAN THATDISSOLVED IN REDUCING CUPRIC TO CUPROUS IONS, BUT NOT MORE THAN SO MUCHAS IS AT LEAST 99.9% CIPPER; COLLECTING PREIPITATED COPPER ANDRECIRCULATING RESIDUAL COPPER TO THE "SOLUTION OPERATIONS".